Steps to troubleshoot SQL connectivity issues

We have been seeing and trying to resolve SQL connectivity issue all the time. I guess it would be helpful if we can put some guidance on how to resolve connectivity issues. Here comes a proposal based on my experience.

Basically, when you failed to connect to your SQL Server, the issue could be:

1) Network issue,

2) SQL Server configuration issue.

3) Firewall issue,

4) Client driver issue,

5) Application configuration issue.

6) Authentication and logon issue.

Usually, customers see connectivity issue in their applications, but it would be great if you can follow the steps below to eliminate issues one by one and post a question on SQL Server Data Access forum if needed.

Step 1: Network issue

You might be able to make local connection without a working network, but that's a special case. For remote connection, a stable network is required. The first thing to trouble shoot SQL connectivity issues is to make sure the network we rely on is workable and stable. Please run the following commands:

nslookup(type your local and remote machine name and IP address multiple times)

Be careful to see any mismatch on the returned results. If you are not able to ping your target machine, it has high chance that either the network is broken or the target machine is not running. It's possible the target machine is behind a firewall and the firewall blocks the packets sent by ping, though. Windows firewall does not block ping (ECHO) packet by default. The correctness of DNS configuration on the network is vital to SQL connection. Wrong DNS entry could cause of all sorts of connectivity issue later. See this link for example, "Cannot Generate SSPI Context" error message, Poisoned DNS.

Step 2: SQL Server configuration issue

You need to make sure the target SQL Server is running and is listening on appropriate protocols. You can use SQL Server Configuration Manager (SCM) to enable protocols on the server machine. SQL Server supports Shared Memory, Named Pipes, and TCP protocols (and VIA which needs special hardware and is rarely used). For remote connection, NP and/or TCP protocols must be enabled. Once you enabled protocols in SCM, please make sure restart the SQL Server.

You can open errorlog file to see if the server is successfully listening on any of the protocol. The location of errorlog file is usually under:

%ProgramFile%Microsoft SQL Server/MSSQLxx.xxx/MSSQL/Log

If the target SQL instance is a named instance, you also need to make sure SQL Browser is running on the target machine. If you are not able to access the remote SQL Server, please ask your admin to make sure all these happen.

Step 3: Firewall issue

A firewall on the SQL Server machine (or anywhere between client and server) could block SQL connection request. An easy way to isolate if this is a firewall issue is to turn off firewall for a short time if you can. Long term solution is to put exception for SQL Server and SQL Browser.

For NP protocol, please make sure file sharing is in firewall exception list. Both file sharing and NP use SMB protocol underneath.

For TCP protocol, you need put the TCP port on which the SQL Server listens on into exception.

For SQL Browser, please put UDP port 1434 into exception.

Meanwhile, you can put sqlservr.exe and sqlbrowser.exe into exception as well, but this is not recommended. IPSec between machines that we are not trusted could also block some packets. Note that firewall should never be an issue for local connections.

Step 4: Client driver issue

At this stage, you can test your connection using some tools. The tests need to be done on client machine for sure.

First try:

telnet <your_target_machine> <TCP_Port>

You should be able to telnet to the SQL server TCP port if TCP is enabled. Otherwise, go back to check steps 1-3. Then, use OSQL, SQLCMD, and SQL Management Studio to test sql connections. If you don't have those tools, please download SQL Express from Microsoft and you can get those tools for free.

SQLCMD also applies here. In addition, you can use “-Stcp:Your_target_machine, Tcp_port” for TCP, “-Snp:Your_target_machineYour_instance” for NP, and “-Slpc:Your_target_machineYour_instance” for Shared Memory. You would know if it fails for all protocols or just some specific procotols.

At this stage, you should not see general error message such as error 26 and error 40 anymore. If you are using NP and you still see error 40 (Named Pipes Provider: Could not open a connection to SQL Server), please try the following steps:

If you get failure in b), it's very likely you have OS/Network configuration issue, which is not SQL Server specific. Please search on internet to resolve this issue first.

You can try connection using both Windows Authentication and SQL Authentication. If the tests with all tools failed, there is a good chance that steps 1-3 were not set correctly, unless the failure is logon-related then you can look at step 6.

If you succeeds with some of the tools, but fails with other tools, it's probably a driver issue. You can post a question on our forum and give us the details.

You can also use “windowssystem32odbcad32.exe” (which ships with Windows) to test connection by adding new DSN for various drivers, but that's for ODBC only.

Step 5: Application issue

If you succeed with steps 1-4 but still see failure in your application, it's likely a configuration issue in your application. Think about couple of possible issues here.

a) Is your application running under the same account with the account you did tests in step 4? If not, you might want to try testing in step 4 under that account or change to a workable service account for your application if possible.

This is probably the most difficult part for sql connectivity issues. It's often related to the configuration on your network, your OS and your SQL Server database. There is no simple solution for this, and we have to solve it case by case. There are already several blogs in sql_protocols talking about some special cases and you can check them see if any of them applies to your case. Apart from that, things to keep in mind:

b) Make sure your login account has access permission on the database you used during login ("Initial Catalog" in OLEDB).

c) Check the eventlog on your system see if there is more information

At last, please post question on our forum. More people could help you over there. When you post question, you can refer to this link and indicate you see failure at which step. The most important things for us to troubleshoot are a) exact error message and b) connection string.

Xinwei Hong, SQL Server ProtocolsDisclaimer: This posting is provided "AS IS" with no warranties, and confers no rights

Hi, I am having below error in my production server that running ASP.NET2.0 and SQL Server 2005. Can someone tell me why this error happen? Thanks.

Source = .Net SqlClient Data Provider

Error = A connection was successfully established with the server, but then an error occurred during the pre-login handshake. (provider: SSL Provider, error: 0 – Not enough storage is available to complete this operation.) | at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)

at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)

I am having occasional/rare connection problems with ADO/ADO .Net connection pooling. The connections use aliases set up for TCP/IP. Could the problems be occurring because of Kerberos Ticket Expiration with the pooled connections or could it be that SQL Server is Orphaning the pooled connections or could it be some sort of socket problem? Perhaps someone has another suggestion as to what may be wrong. I am considering using Named Pipes instead to get around Kerberos authentication.

I’ve also found that running a quick trace to catch login failures is useful. App teams generally don’t believe that their app is configured wrong. They will insist that the server is down even though all connectivity tests we use work. We will start the trace and have them try to connect. If you don’t see a failure, you can absolutely point to a problem outside of MSSQL. It sometimes takes this to get folks to check other possibilities.

I’m having an issue connectiont to SQL server through Access. It only occurs during testing when we set the PC date forward on the client machine. Has anyone come accross this? ErrorMsg: -2147467259 Cannot generate SSPI Context

We’re seeing an issue in our environment where we have a .NET 1.1 web application on a Windows 2003 server machine and SQL Server on a Windows 2000 server machine. In the application, we use SQL logins to connect to the db. What we are seeing is, when we put a bad password to log in, an error message is generated (login failed) in the event log which is what’s expected, but then we continually see the same error message repeating for the next few hours as if the connection is still alive and retrying automatically. Any ideas why? Thanks

I am trying to connect to a MSSQL 2005 server from a Windows NT box through a system DSN. I know 2005 prefers you use SQL Native Client to connect, however, all that is on this machine is the SQL Server driver. How can I make this work?

A connection attempt failed because the connected party did not properly respond after a period of time, or established

connection failed because connected host has failed to respond.

This still looks like a firewall issue if the server name is correct. Did you tried to follow my steps to troubleshoot? Is your server machine Vista/Windows Server 2008? Turning off the firewall on Vista/W2k8 is little tricky as it involves different domains.

I would suggest you post your follow up question on our forum (mentioned at the end of the blog)

"Message:[Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified ".

Just to brief about my setup , It goes like this;I have a SQL server 2008 installed on Win 2008 (x64)and I also have a clinet machine installed with Win 2003(32-bit).

Now I am trying to establish a connectivity between them by using SNAC tool (v10.0).

Actually I am running one benchmark application script on Client machine which first tries to establish the database connectivity .

Now I think some one can give me some clue what could be the reason for the error.I also have created Aliases on both server as well as Client machine (Was not very sure where they required to be created).

I have been strugling all alone for quite a time now.Hope someone can help me to reach at the solution.

"[DBNETLIB][ConnectionOpen (Connect()).]SQL Server does not exist or access denied"

While accessing SQL Server 7.0 from a MS Access 2007 application. My client m/c OS: Windows XP Service Pack 2. The same access application is working on other desktop (XP SP2) in the same network. I have performed the following steps, but no hope.

#1: I found sqloledb.rll file was missing, i placed the above resource file in appropriate location. No luck.

OLE DB provider "SQLNCLI" for linked server "oa-citrix02" returned message "An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections.".

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Server: Msg 50000, Level 16, State 1, Line 15

Named Pipes Provider: Could not open a connection to SQL Server [5].

OrangeNamed Pipes Provider: Could not open a connection to SQL Server [5].

I seem to be in deep trouble over a linked server setup. I have 2 servers running SQL server 2005 standard x64 SP3. I am trying to create a linked server from one to another.

I createa link server and map a login called testuser2 (sql login) on both servers, and has sysadmin permissions. However, after running sp_addlinkedserver and sp_addlinkedsrvlogin, if I attempt running a query or run "Test Connection" the query times out or gives an error " login failed for NT AUTHORITYANYONYMOUS LOGON..with the client name.

If I check in the server logs (to which I was trying to query ), it gives me an error

Error: 18456, Severity: 14, State: 11.

I tried pinging and doing an nslookup from client machine and it succeeds. These are servers on same domain and in the same location. I have also ensured that both servers have named pipes enabled on them..

I also sometimes get error 7399. Linked server authentication failed, even through I can connect remootely through the same login ‘testuser2’ on either server.

Thank You so much Keik. You helped determine the last port I had to unblock. I am running SQL 2008 on WS 2008. For anyone else having this issue for me I did this.

On my Windows Server 2008 I did the following:

1.Added an exception for the SQL Browser exe file.

2.Added an exception for the UDP Port 1434.

3.Found out what the listening port was by following Keik’s advice which is

"Look in the registry using regedit.exe at HKEY_LOCAL_MACHINESOFTWAREMicrosoftMicrosoft SQL ServerSQLEXPRESSMSSQLServerSuperSocketNetLibTcp.

One of the nameValue pairs has name TcpPort and a value, which is the port that the SQL Server is listening on (mine was set to 1030)."

Mine was 51070 then added the exception to that tcp in the windows firewall.

Then boom all access finally granted. Thank you Keik for suggesting that as it finally became unblocked and now works like a champ. I have spent litterally 2 days getting this to work and I had figured that it was a simple firewall issue but was lost on where to find the information. God Bless you Sir!

I have a java program which takes connection from database connection string is :

"jdbc:sqlserver://localhost:1434;databaseName=abc"

when i ru this iit works fine. I modified the code now it takes connection and with out closing it tries to take another connection second time it throws an exception msg saying:: "An I/O error occurred while receiving the TDS prelogin response."

I thought its because of maximum no of connection but maximum no of conn is set to 0(ulimited).

"To guarantee that there are resources available for the connection, only one DAC is allowed per instance of SQL Server. If a DAC connection is already active, any new request to connect through the DAC is denied with error 17810."

Currently we have installed Windows operating server 2008 and SQL server 2008 and now i want to connect server and workstation,unfortunately im unable to see SQL SERVER native client 10.1 at in ODBC connectivity.If i select SQL SERVER then it’s prompting me "Login user failure :ABCServerGuest" in ODBC section.

1) do i need to install any package to all workstation/client pc?

2) Can i connect directly using SQL Server setting to connect to server and database?

I traced it, but I didn’t find the character (I didn’t write the character ‘-‘). I ran my app on different computers, there’s no problem with my app. I reformatted my computer and reinstalled all the programs, it didn’t work. It still had that error…

Can someone tell me what’s wrong with my application (or computer)??

Note: I’m using VB6 for the interface and SQLServer 2000 for the database and crystal report for report view. the error occurs when view reports using crystalr report.

I traced it, but I didn’t find the character (I didn’t write the character ‘-‘). I ran my app on different computers, there’s no problem with my app. I reformatted my computer and reinstalled all the programs, it didn’t work. It still had that error…

Can someone tell me what’s wrong with my application (or computer)??

Note: I’m using VB6 for the interface and SQLServer 2000 for the database and crystal report for report view. the error occurs when view reports using crystalr report.

Intermittent connectivity issues between application servers and sql cluster , i have 3 application servers are on NLB and 2 database severs configured on SQL cluster [SQL 2005] . i am facing a intermittent connectivity issues with one of the application server (in NLB) to the db cluster . If anybody faced like this scenario before please let me know the resolution . Your advises is highly appreciable………

i am using windows server 2008 r2 64 bit operating system and i've installed sql server 2008 standard edition 32 bit in that. my application is working properly in server system . but, while accessing from client its not working properly. so, i've tested with .udl at client machine . it's raising an error as [DBNETLIB][Connection Open(Connect()).]SQL Server does not exist or access denied. i was using xp2 in client machine. please give me the solution so that i can start the work at client side.

With all the data moving into the "cloud" I was wondering if someone could point me to some good resources reguarding trying/catching specific SQL server events… such as trapping: (TSQL 2008r2 server) "Msg 6005, Level 14, State 2, Line 1 SHUTDOWN is in progress." Plus any ideas for handling basic connectivity issues programatically.

Right now my focus is on web development using C# (ASP4.NET/MVC) and MS Access 2010 dev (using VBA 7.0).

I am having problem running the sqlcmd command in my linux box with an error "Unable to load SQLCMD resource file(s)". After investigating this I realized that the driver and sqlcmd are looking for the resource files at a specific path /opt/microsoft/msodbcsql location. In my environment this is not possible:

1) I am not an admin and can not access to that directory

2) We use enterprise file system so individual machine installation directory is not allowed.

Is it possible to have the driver look at some other location for resource files?

Hi – I set up a test and production instance SQL Server 2008 R2 Express.

The test I installed on the default c: drive and works fine. The production I installed the data on the e: drive and I can't get to it. However the application works fine from the production server. Any Ideas?

I am not able to connect to SQL 2005 DB in windows authentication,plz help me out…i'm gtng an error as follows….

ADDITIONAL INFORMATION:

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 25 – Connection string is not valid) (Microsoft SQL Server, Error: 87)

I have an ASP.NET/IIS 6 based application that runs on a SQL Server 2000 database on Windows 2003. We lost the server and we are trying to setup the application from scratch in a new machine. The application fails with error 40 and also error 26 (cannot locate SQL Server connection). The application and the database are on the same host. No local firewall is running. The OSQL utility works correctly. If I install the IIS application in another machine, that application is actually capable to connect to the database (the connection error happens locally only).

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 0 – No connection could be made because the target machine actively refused it.) (Microsoft SQL Server, Error: 10061)